Exoplanet WASP-18b Has a Smothering Stratosphere Dominated by Carbon Monoxide

Posted on December 4, 2017

WASP-18b has a stratosphere loaded with carbon monoxide. There are no signs of water. The exoplanet is located 325 light-years from Earth. WASP-18b has a mass 10 times that of Jupiter. It orbits its star once every 23 hours. It has been observed using NASA's Spitzer and Hubble space telescopes.

Kyle Sheppard of NASA's Goddard Space Flight Center in Greenbelt, Maryland, is the lead author of the paper published in the Astrophysical Journal Letters. Sheppard says, "The composition of WASP-18b defies all expectations. We don't know of any other extrasolar planet where carbon monoxide so completely dominates the upper atmosphere."

Nikku Madhusudhan, a co-author of the study from the University of Cambridge, United Kingdom, says, "The only consistent explanation for the data is an overabundance of carbon monoxide and very little water vapor in the atmosphere of WASP-18b, in addition to the presence of a stratosphere. This rare combination of factors opens a new window into our understanding of physical and chemical processes in exoplanetary atmospheres."

The study's findings indicate WASP-18b has hot carbon monoxide in the stratosphere and cooler carbon monoxide in the layer of the atmosphere below (the troposphere). The researchers detected two types of carbon monoxide signatures, an absorption signature at a wavelength of about 1.6 micrometers and an emission signature at about 4.5 micrometers. This marks the first time researchers have detected both types of fingerprints for a single type of molecule in an exoplanet's atmosphere.

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